Ultrasonic measurement apparatus having a deflection unit forming a loop

ABSTRACT

An ultrasonic measurement apparatus ( 10 ) for measuring the flow velocity of a fluid is provided which flows in a pipeline in a main flow direction, wherein the ultrasonic measurement apparatus ( 10 ) has an ultrasonic measurement zone ( 36 ) with at least a pair of ultrasonic transducers ( 38 ), an evaluation unit for determining the flow velocity from a propagation time difference of ultrasound transmitted and received with and against the flow, as well as a deflection unit, by means of which the fluid from the main flow direction is deflectable and suppliable to the ultrasonic measurement zone ( 36 ). In this respect the deflection unit ( 20, 26, 32 ) forms a loop.

The invention relates to an ultrasonic measurement apparatus and to amethod for the measurement of the flow velocity.

Fluid velocities in pipelines and passages can be determined by means ofultrasonic measurement techniques in accordance with the propagationtime difference method. In this respect ultrasonic pulses aretransmitted and received by a pair of ultrasonic transducers which areoppositely disposed at walls of the pipeline, at the end of ameasurement path, transverse to the flow direction of the fluid. Theflow velocity is determined in the flow direction and in the oppositedirection against the flow from the propagation time difference of theultrasound in the measurement path. In this respect the ultrasonictransducers alternatively work as a transmitter and as a receiver. Theultrasonic signals transported by means of the fluid are accelerated inthe flow direction and are decelerated against the flow direction. Theresulting propagation time difference is calculated to a mean flowvelocity with reference to geometric quantities. An operation volumeflow also results which is frequently the interesting measurementquantity for fluid calculated by volume from the cross-sectional area.

This known measurement principle is illustrated in FIG. 7. As anessential component of a common measurement apparatus 110 two ultrasonictransducers 118, 120 are arranged at an angle in the walls of thepipeline 112 in which a fluid 114 flows in the direction of the arrow116. The ultrasonic transducers 118, 120 alternatively work astransmitters and as receivers. The ultrasonic signals transported by thegas are accelerated in the flow direction and are decelerated againstthe flow direction. The resulting propagation time difference iscalculated to a mean flow velocity with reference to geometric sizes.The operational volume flow results from the cross-sectional area. Thegeometric ratios are described by the following variables:

v: flow velocity of the fluid in the pipeline L: length of themeasurement path between the two ultrasonic transducers α: angle, atwhich the ultrasonic transducers transmit and receive Q: volume flow D:diameter of the pipeline t_(v): propagation time of the ultrasound withthe flow t_(r): propagation time of the ultrasound against the flow

From this the following relationships result for the sought afterquantities v and Q:v=L/(2 cos α)(1/t _(v)−1/t _(r)) andQ=v¼D ²π.

An important and challenging field of application is gas counters fornatural gas pipelines where the smallest deviations in the measurementaccuracy already lead to significant marked values due to the immenseamount of gas conveyed and the value of the raw material. Ultrasonicflow meters are increasingly being used in the field of large quantitygas measurement due to their measurement accuracy, freedom frommaintenance, and self-diagnostic possibilities on gas transport and gasstorage. In the field of distribution, however, the cost pressure withregard to established technologies such as turbine wheel flow meters androtary displacement gas meters is still too high.

To satisfy the requirements for measurements subject to legal controlwith regard to the achieved accuracy, a very high effort in work andcost is namely required. As an ultrasonic measurement path only scansthe flow velocity at defined positions, the mean flow velocity issubsequently only extrapolated for the overall cross-section. For thisreason, higher accuracies can only be achieved when the flow can bereproduced well and/or when an undisturbed flow profile is present orwhen a plurality of measurements paths is capable of resolving theseirregularities. To achieve higher accuracies, the flow profile can beinfluenced specifically, for example by means of flow rectifiers orlong, straight inlet paths. However, the flow rectifiers are only in theposition to uniformly establish the flow in a limited manner and long,straight inlet paths require a lot of construction space and are notalways available. A measurement at a plurality of measurement pathsrequires a correspondingly complex measurement apparatus.

Particularly in the use of ultrasonic measurement apparatus in the fieldof distribution the installation typically occurs in gas pressureregulating stations, in which the medium pressure or high pressure ofthe transport pipeline is reduced to the low pressure or medium pressureof the distributor network. This reduction occurs via regulating valvesand such components produce interference sound in the ultrasonic regionwhich can be superimposed onto the actual measurement signals and thusinfluence the measurement accuracy.

This generally means that the user of common ultrasonic measurementapparatus has the disadvantage that additional installations have to becarried out which bring about increased costs and component sizes.

Beside the ultrasonic measurement technique, mechanical turbine wheelgas meters or rotary displacement gas meters are used for gasmeasurement. Also variants are present, in which the flow is deflectedfor the counter and redirected into the pipeline following themeasurement. The formation of the flow is generally indifferent formechanical measurements so that the interference of the original flowand flow direction can be considered without a problem. For ultrasoniccounters one, however, always strives to mount these preferablyfollowing a very long and straight calming section so that the flow canbe made uniform and to support the flow by means of the flow rectifier.Furthermore, the ultrasonic counters themselves are also mounted andconfigured such that the fluid can flow as freely and undisturbed aspossible.

The mechanical mode of measurement of these counters, moreover, has thedisadvantage that they are movable and thus susceptible and prone towear parts are arranged directly in the flow. Furthermore, thediagnostic properties are missing which can be achieved in theultrasonic counter by monitoring additional measurement quantities. Thestatus of the measurement apparatus or the measurement process can thusnot be monitored and analyzed and/or a very cost-demanding andtime-demanding examination is respectively required for this. Due to thelacking diagnostic possibilities and thus the lacking control over themeasurement accuracy this is unsatisfactory for the operator alreadybecause small deviations in accuracy can correspond to high values.

From DE 10 2005 062 629 A1 an ultrasound-based water counter fordomestic use is known. In this respect the water is radially deflectedfrom the flow and guided through a measurement chamber back into theflow via an exit region. The measurement chamber forms a ring whoseplane lies parallel to the flow direction in the pipeline. Ultrasoundpropagates through the ring with the aid of numerous elaboratelydeflecting reflectors. The measurement chamber is provided with aplurality of elaborately drafted protrusions and openings to generate auniform ring flow which in accordance with the teaching of DE 10 2005062 629 A1 should also ensure that the reflectors are ideally scavengedto prevent air bubbles so that the measurement is not influenced. Thedesign of the measurement chamber and thus of the flow paths and of thesound paths in its interior are thus very elaborate. Additionally to thecosts which such components bring about, the ultrasonic measurement mustalso be set extremely accurately to these complicated parts on the useof the common ring principle in gas pipelines, wherein one can only fallback on the experiences of common ultrasonic measurement devices, whichare directly arranged in the non-deflected main flow, in a limitedmanner.

U.S. Pat. No. 4,506,552 describes an ultrasonic through-flow measurementdevice for highly viscous and/or deeply cold fluids. To prevent bubblesdue to temperature gradients and the resulting turbulences themeasurement path lies within a double tube so that fluid also flows inthe outer wall and thus simultaneously causes a cooling of themeasurement path. In a variant the coaxial flow path is guided in asuperimposed pipe part.

DE 29 24 561 B1 shows a counter for a domestic water supply having anultrasonic measurement path which in a variant lies perpendicular to theflow direction of the water line, in that a 90° pipeline part directsthe water to the measurement path and a corresponding 90° pipeline partredirects the water back into the waterline.

EP 1 227 303 A2 shows a further ultrasonic through-flow counter, inwhich the fluid is deflected from the line and is deflected into ameasurement path extending parallel to the line. The measurement capsulecan be mounted to a common fitting when used as a water counter.

In EP 1 909 076 A1 a similar basic construction for a through-flow meteris illustrated whose measurement capsule is attached to a connectionfitting and in which an ultrasonic measurement path is realized in apipe parallel to the actual line.

U.S. Pat. No. 4,140,012 discloses an ultrasonic through-flow meter inwhich the measurement path is perpendicular and centrally arrangedwithin the actual line which is increased in diameter in the region ofthe measurement path while a deflector standing at a 45° angle forcesthe fluid to flow through the measurement path by means of a two-timeperpendicular change in direction.

In EP 2 146 189 A1 the flow passage has sharp deflections and abruptchanges in cross-section in an axial embodiment. This has undesiredconsequences for an ultrasonic measurement. The flow falls off in theultrasonic measurement path, back flow regions arise which lead toinstable measurement values, and strong turbulences which complicate thesignal evaluation. Moreover, the pressure loss is very high due to theflow supply. As the allowable pressure loss of the measurement device islimited no pressure reserve remains for a flow conditioning. Theultrasonic transducers are finally arranged in the interior of theinflow region so that the electric contacting has to be achieved by theflowing gas. This requires pressure-resistant feed-throughs.

A further disadvantage of common ultrasonic measurement apparatuses isthe type of fitting. The ultrasonic measurement device is typicallyflanged in place instead of a pipeline section. An exchange ormaintenance is correspondingly elaborate. Such maintenances are alsorequired to regularly check and recalibrate the ultrasonic measurementdevice subject to legal control. In this respect the calibration has totake place in a particular high pressure test stand which by no meanshas to be in close proximity to the position of operation. In thisrespect, the complete counter including the pressure-stable housing hasto be removed from the line be sent in and then be reinstalled. Aninterim operation is only possible when a replacement part calibratedspecifically for this position of application is installed.

FIG. 8 illustrates the common maintenance of an ultrasonic measurementapparatus 200. For this purpose the pipeline section 202 is interruptedor switched pressure-free. To further ensure the supply continues duringthis time, a redundant second line 204 is provided. By changing thebarriers 206 the gas flow is supplied from the pipeline section 202 intothe second line 204 and vice versa.

Through the redundant line construction considerable additional costsarise. The additional cost is particularly uneconomical as thereplacement line is only infrequently used. The typical period of use ofthe ultrasonic measurement apparatus 200 is five or more years andduring the maintenance or an exchange of the ultrasonic measurementapparatus 200 the use of a recalibrated replacement part only takes afew hours.

Following the maintenance the pipeline section 202 has to be re-impingedwith pressure. As in natural gas supply lines explosive and pressurizedmedia are transported, significant safety measures have to be consideredand only specifically trained personal can be used. For this reason highcosts are commonly associated with the maintenance works.

From DE 10 2007 028 431 A1 an ultrasonic counter based on a exchangeableuse is known. The problem of how a pressurized line can be exchangedduring its use is, however, not solved.

EP 2 146 189 A1 also mentions an exchangeable measurement use. Duringwhose reinstallation it must, however, be ensured that the overall gasflows through the measurement section. Due to the inner lyingmeasurement section a leak tightness has to be evidenced between theinflow and the outflow in a very elaborate manner.

For this reason it is the object of the invention to enable an accurateand simple ultrasonic measurement of flow velocities.

This object is satisfied by an ultrasonic measurement apparatus formeasuring the flow velocity of a fluid which flows in a pipeline in amain flow direction, wherein the ultrasonic measurement apparatus has anultrasonic measurement zone with at least a pair of ultrasonictransducers, an evaluation unit for determining the flow velocity from apropagation time difference of ultrasound transmitted and received withand against the flow, as well as a deflection unit, by means of whichthe fluid from the main flow direction is deflectable and suppliable tothe ultrasonic measurement zone, wherein the deflection unit forms aloop.

In a further aspect this object is satisfied by a method for measuringthe flow velocity of a fluid which flows in a pipeline in a main flowdirection, wherein the flow velocity is determined from a propagationtime difference of ultrasound transmitted and received with and againstthe flow from a pair of ultrasonic transducers in an ultrasonicmeasurement zone, wherein the fluid is deflected from the main flowdirection and supplied to the ultrasonic measurement zone for themeasurement, wherein the ultrasonic measurement takes place whilst thefluid is deflected such that it flows in a loop.

In this respect the solution in accordance with the invention is basedon the basic idea that fluid from a main flow direction in the pipelineis to be deflected, for example, into a stub-like attachment. In thisrespect the flow is only deflected by a highest angle at each linedsection and remains as untouched as possible in its cross-section. Thisis achieved by a loop i.e. in a visible manner in a looping or at leastin a flow path which describes a 360° spatial curve. In this way theflow can be measured independently from the line section downstream ofthe ultrasonic measurement apparatus and thus very reproducible. On theother hand, the ultrasonic measurement region is significantly moreaccessible.

The solution in accordance with the invention has the advantage that themeasurement position is reproducibly, acoustically decoupled from theflow profile present at the input of the measurement device and at thesame time an acoustic insulation with respect to previously connectedinterference sound sources is achieved, for example, with regard topressure-regulating valves. Only a marginal pressure loss arises so thatsufficient pressure reserves are present for a flow conditioning. Theultrasonic measurement apparatus has a very small installation lengthand due to its reproducible flow properties makes do with a minimumnumber of ultrasonic measurement paths.

In this respect all advantages of the ultrasonic measurement withrespect to mechanical measurement principles such as rotary displacementgas meters or turbine wheel counters is achieved including all of thepreviously mentioned advantages such as stable measurement values for alarge through-flow region. The flow supply in accordance with theinvention enables a modular construction of the ultrasonic measurementapparatus. In this respect a pressurized or a pressure-free ultrasonicmeasurement region and/or an ultrasonic measurement region for highpressure and low pressure can be designed with free constructive layoutin view of the material selection, wall thicknesses and type ofultrasonic transducer. As the ultrasonic measurement region is easilyaccessible, the tightness both for the environment and also between theinflow and the outflow can be easily accounted for. Furthermore, theultrasonic transducers themselves are easily accessible and thus simplyand cost-effectively contactable. Despite of these advantages theultrasonic measurement apparatus allows a construction which can bemanufactured cost-effectively.

The loop preferably has a first deflector, an inflow region, an arc, anoutflow region and a second deflector so that fluid from the main flowdirection is deflectable into the inflow region by means of the firstdeflector is deflectable from there into the outflow region andsubsequently is deflectable back into the main flow direction by meansof the second deflector, wherein, in particular, the first deflector andthe second deflector form a right angle, and the arc forms an angle of180°. All these angles must not necessarily be accurately abided to, forexample, for the deflections also an angular region of 80°-100° or evena larger angular region is plausible. For such deviations, however,abrupt changes of direction and as a whole a too unwieldy constructiondesign should be prevented. Corresponding angular deviations are alsoplausible for the 180° arc. In this respect the angles must add up to360° so that the fluid can flow again in the main flow directionfollowing the flow through the ultrasonic measurement apparatus. A smallcontribution to this overall angle can also be made by the inflowregions and the outflow regions which could deviate from a straightshape. It should, however, be noted that the loop is a three-dimensionalgeometric form so that the condition of flowing longitudinally andtransversely back into the initial direction must be satisfied.

The inflow region and the outflow region preferably each have a partialregion arranged adjacent to one another and are aligned in parallel toone another, wherein, in particular, a plane, which includes bothstraight partial regions, is perpendicular to the main flow direction.Within the inflow region and the outflow region thus no interfering flowdeflections are present. Through the parallel arrangement the flowcross-section can be maintained constant in contrast, for example, to aconcentric arrangement. In that the mentioned plane is arranged in thementioned manner, a loop practically arises both in the longitudinaldirection and also in a direction transverse to the direction of thepipeline. Thus a particularly uniform and symmetric flow supply and aparticularly compact construction of the ultrasonic measurementapparatus can be achieved.

The loop is preferably designed smooth and without sharp changes indirection or constrictions, wherein, in particular, the arc has a wallcontour which causes a specific flow break-away in a zone uncritical forthe ultrasonic measurement. A sufficiently calm flow profile can thus beformed in the ultrasonic measurement region. Furthermore, the pressureloss remains minimal. The specific wall contour in the arc causes aspecific flow break-away in a region uncritical for the ultrasonicmeasurement. In the ultrasonic measurement region a uniformation of theflow profile is achieved and interfering swells and backflow regions areprevented. Thus also a measurement for high flow velocities and thus asignificant enlargement of the measurement region is possible.

A flow rectifier is preferably provided in the inflow region and/or inthe outflow region. This additionally ensures a reproducible flow andthus, a higher measurement accuracy. In particular on arrangement in theinflow region sufficient space also for more complex flow rectifiers isavailable and also sufficient path length is available for auniformation due to the subsequent flow path up to the ultrasonicmeasurement path. Due to the flow supply in accordance with theinvention sufficient pressure reserves are present for the flowrectifier.

The ultrasonic measurement zone is preferably provided in the outflowregion, in particular with sufficient separation to the arc so that theflow is reproducibly stabilized on entry into the ultrasonic measurementzone. In this respect even more preferably straight partial sections arearranged before the outflow region and/or following the ultrasonicmeasurement zone. At the point in time of the ultrasonic measurement thefluid has then already passed a substantial portion of the loop and isthus particularly effectively decoupled from interferences upstream fromthe ultrasonic measurement apparatus. This is even truer when a flowrectifier is arranged in the inflow region. Additionally oralternatively, however, a flow rectifier can also be arranged in theoutflow region.

The ultrasonic transducers are preferably arranged in the ultrasonicmeasurement zone such that the transmitted and the received ultrasoundhas at least a component in a direction transverse to the flow. In thisway the ultrasonic transducers can be mounted sidewise. The counter-partto such an embodiment with a measurement transverse to the flow areultrasonic transducers which are arranged longitudinally, for example,at the top of the output of the arc and at the bottom of the flowoutput. This is ineffective because non-calming flow parts areintroduced into the measurement which leads to less accurate and lessreliable measurement values.

The ultrasonic measurement apparatus preferably has a pipe shaped basepiece having connection regions, in particular flanges for the pipelinewhich includes the first deflector and the second deflector. This basepiece is compatible to the standard insertion length, for example ofturbine wheel counters or of rotary displacement gas meters and aremanufactured in different nominal width and with different connectionflanges which are required for the respective pipeline. Following themounting the base piece constantly remains in the pipeline and canthereby be separable functionally and constructively from themeasurement section as a base housing. Thus a simple to manufacture andassembly-friendly measurement attachment can be manufactured.

The ultrasonic measurement apparatus preferably has at least one add-onmodule which each have an extension piece for the inflow region and anextension piece for the outflow region and which are connectable to thebase piece or to the outflow region and which are connectable to thebase piece or to any other add-on module and are separable from the basepiece or from the other add-on module, wherein a final add-on moduleincludes the arc. In the embodiment having the lowest number of add-onmodules only the single final add-on module is thus provided with thearc. In the final add-on module, the extension pieces can also only beprovided in a suggested manner and be provided as very short.

Through the add-on modules additional component groups can be mounteddepending on their need. These can, for example, enable a deflection ofthe flow, cause an additional conditioning of the flow or enableadditional measurement tasks. The outer dimensions of the ultrasonicmeasurement apparatus in the pipe axis, i.e. in the main flow directionare not changed through the add-on modules, as the actual installationlength is determined purely through the geometric dimensions of the basepiece. For this reason, the ultrasonic measurement apparatus can beinstalled compatible to the gas counters users used so far. The add-onmodules can be exchanged simply and upwardly without the base piecehaving to be removed from the pipeline. The flow direction in theultrasonic measurement apparatus is characterized primarily by the loopwithin the add-on module and can for this reason be largely freelydesigned without having to interact within the pipeline. The modularconstruction comprising a base piece and add-on modules allows aflexible and cost-effective manufacture, mounting, change andmaintenance of the ultrasonic measurement apparatus.

The ultrasonic measurement apparatus preferably includes at least oneadd-on module designed as a measurement module having the ultrasonicmeasurement zone and, in particular also includes the flow rectifier.The measurement module can be pre-calibrated outside of the pipeline. Onan exchange of the ultrasonic measurement apparatus the base piece thenremains the pipeline and the present measurement module is exchangedagainst a pre-calibrated measurement module. The design of theultrasonic measurement zone and of the flow conditioning is thusindependent from the base piece and can arbitrarily be varied. Themeasurement value can be configured identically for each nominal widthof the pipeline, although, on the other hand, also adaptations areplausible. Further, or alternative measurement modules can be provided,for example a redundant measurement module for the duration of theexchange, but also different measurement modules for different pressureconditions, for other combinations of the fluid and such like.

The ultrasonic measurement module preferably has an add-on moduleconfigured as a bypass module having a transverse line between theinflow region and the outflow region or a transverse line integratedinto the base piece, wherein a bypass deflector is provided which in oneposition selectively closes the flow to the transverse line and from thetransverse line and releases the flow to the inflow area and from theoutflow area and in another position selectively closes the flow to theinflow region and from the outflow region and releases the flow to thetransverse line and from the transverse line. With the aid of thetransverse line the volume flow can be deflected such that a differentadd-on module is mountable and demountable in a pressure-free manner,for example, as a measurement module. The fluid flow, for example, thegas flow to the user is in this respect not interrupted. Thus additionalconstructive measures at the pipeline, such as blocking devices, bypasslines, venting means or such like can be omitted and this leads to aconsiderable reduction of the plant costs. During the maintenance workthe pipeline itself remains pressurized at the operational pressure. Asno venting and filling of the pipeline section to be maintained isrequired, the duration of the maintenance is reduced. Furthermore,because the base piece remains in the pipeline no elaborate tightnesstests are necessary on restarting the stretch of the pipe. In thisrespect the bypass line can be integrated into the base piece.Alternatively, an individual bypass module can be provided.

The bypass module is configured such that during measurement operationthe flow to the remaining modules and, in particular to the measurementmodule is hardly influenced. Through this no additional measures inthese modules is necessary to ensure their faultless function and anundisturbed measurement. Because of the modular setup the bypass modulefits to the other add-on modules or to the base piece. Also a subsequentfitting of the bypass module into an already installed ultrasonicmeasurement apparatus is possible.

The bypass deflector is preferably configured on the principle of athree way tap, in particular has two spheres perforated in T-shape withseals which are coupled amongst one another and are thus commonlytransferable from the one position into the other position. The selecteddeflection of the flow in the transverse line, for example, for theexchange of an add-on module arranged above or back in the overall loopof the ultrasonic apparatus is very easily and reliably possible, forexample by means of a lever at the outer side. The simple actuation ofthe spherical tap-like construction does not require any in-depthknowledge and for this reason an exchange of add-on modules is alsopossible with lesser trained safety technical personal. Alternatively toa bypass deflector working on the principle of a three way tap, otherforms of valves, gates, flaps and such like are plausible.

The ultrasonic measurement apparatus preferably has an add-on moduleconfigured as a calibration module with at least one pair of ultrasonictransducers for a plausibility check or calibration of the measurementvalues of the ultrasonic measurement zone. The calibration moduletherefore serves as a reference module or a measurement module.

Preferably the use of the ultrasonic measurement apparatus in accordancewith the invention is as a gas counter in a gas pipeline. In thisrespect the mentioned advantages are particularly effective to ensure areliable measurement independent, as far as possible, from the positionof operation and to ensure that the measurement is sufficient to besubjected to legal control.

The method in accordance with the invention can be furthered in asimilar manner and in this respect has similar advantages. Suchadvantageous features are exemplary but not conclusively described inthe dependent claims dependent on the independent claims.

The invention will be described in detail in the following also in viewof further features and advantages by way of example with reference toembodiments and with reference to the submitted drawing. The Figures ofthe drawing show in:

FIG. 1 a a three-dimensional outer view of a first embodiment of anultrasonic measurement apparatus in accordance with the invention;

FIG. 1 b a longitudinal section of the ultrasonic measurement apparatusin accordance with FIG. 1 a;

FIG. 1 c a cross-section of the ultrasonic measurement apparatus inaccordance with FIG. 1 a in the viewing direction onto a base piece;

FIG. 1 d a cross-section analog to FIG. 1 d with an opposing viewingdirection onto a measurement section;

FIG. 1 e a sectional illustration of the ultrasonic measurementapparatus in accordance with FIG. 1 a transverse to a known flowdirection of the fluid;

FIG. 2 a a three-dimensional outer view of a second embodiment of anultrasonic measurement apparatus in accordance with the invention havinga bypass;

FIG. 2 b a longitudinal section of the ultrasonic measurement apparatusin accordance with FIG. 2 a,

FIG. 2 c a sectional illustration of the ultrasonic measurementapparatus in accordance with FIG. 2 a transverse to a main flowdirection of the fluid;

FIG. 3 a a three-dimensional outer view of a second embodiment of anultrasonic measurement apparatus in accordance with the invention havinga bypass and a reference measurement section;

FIG. 3 b a longitudinal section of the ultrasonic measurement apparatusin accordance with FIG. 3 a;

FIG. 3 c a sectional illustration of the ultrasonic measurementapparatus in accordance with FIG. 3 a transverse to a main flowdirection of the fluid;

FIG. 4 a a three-dimensional outer view of a bypass module;

FIG. 4 b a longitudinal section through the bypass module in accordancewith FIG. 4 a;

FIG. 5 a a three-dimensional outer view of a calibration module;

FIG. 5 b a longitudinal section through the bypass module in accordancewith FIG. 5 a;

FIG. 6 a a sectional illustration of a base piece having an integratedbypass line, wherein the bypass line is closed and the fluid flowsthrough the measurement section;

FIG. 6 b a sectional illustration in accordance with FIG. 6 a for anopen bypass line and a pressure-less measurement section;

FIG. 7 a common arrangement of two ultrasonic transducers transverse toa flow direction of a fluid for the explanation of the measurementprinciple; and

FIG. 8 a common pipeline arrangement having a redundant pipe supply fordeflecting the fluid during an exchange of an ultrasonic measurementapparatus.

FIG. 1 shows a first embodiment of an ultrasonic measurement apparatus10 in accordance with the invention in different views. In this respectFIG. 1 a is a three-dimensional outer view, FIG. 1 b is a longitudinalsection, FIG. 1 c is a cross-section in the viewing direction down ontoa base piece 12, FIG. 1 d is a cross-section in the viewing directionupwards onto a measurement module 14 and FIG. 1 e is a sectionalillustration transverse to a main flow direction, i.e. the longitudinalaxis of the base piece 12.

The base piece 12 has flange regions 16 by means of which it is mountedinto an existing pipeline in which it replaces a corresponding pipelinesection. Alternatively, also a different attachment means, such as athread can be provided. A fluid flows in the pipeline in its axialdirection which is referred to as the main flow direction, for example,natural gas flows in a gas pipeline. With the aid of a releasableconnection 18 the measurement module 14 is mounted onto the base piece18. In an alternative embodiment base piece 18 and measurement 14 canalso be formed as one piece.

The ultrasonic measurement apparatus 10 shifts the measurement from thepipeline into an axis transverse to the main flow direction and, inparticular perpendicular to the main flow direction. For this reason theflow is supplied without abrupt changes of direction and withoutcross-sectional constrictions in a loop, as is respectively indicated inthe FIGS. 1 a-e by means of an arrow and will be described in detail inthe following.

The inflowing fluid is deflected in a first deflector 20 from the mainflow direction about 90° sidewise and upwardly in the base piece 12 andexits from the base piece 12 via a first opening 22. It flows through afirst straight partial section 24 and is subsequently deflected in a180° arc 26 into the opposite direction in which it passes the secondstraight partial region 28 which is arranged parallel to the firstpartial region 24. The fluid then reenters into the base piece 12through a second opening 30 beside the first opening 22 where it isdeflected by a second deflector 32 again by 90° sidewise downwardly backinto the main flow direction and thus leaves the ultrasonic measurementapparatus 10 into the pipeline.

A flow rectifier 34 is arranged in the first straight partial region 24in the measurement module 14. The flow rectifier 34 is configured in amanner known per se and ensures that in the inflow a uniformed flow isformed and enters into the arc 26. The parallel second partial region 28more specifically the anti-parallel second partial region 28 includes anultrasonic measurement zone 36 in which two pairs of associatedultrasonic transducers 38 respectively span an ultrasonic measurementpath 40. In principle, also a pair of ultrasonic transducers 38 withonly one measurement path 40 can be used, but for reasons ofstandardization typically at least two measurement paths 40 are used.Further measurement paths 40 are plausible to further improve themeasurement accuracy for remaining discrepancies in the flow. Anon-illustrated evaluation unit which is arranged, for example, as apart of a measurement module 14 at the ultrasonic transducer 38 or inthe outer wall of the measurement module 14, generates ultrasound andevaluates the received ultrasonic signals in accordance with the methoddescribed in the introduction and from a propagation time differencedetermines the flow velocity of the fluid.

In all flow regions sharp changes of direction and flow constrictionsare prevented. This is also true for the region of the arc 26 in whichthe flow is supplied behind the flow rectifier 34 back to the ultrasonicmeasurement zone 36. However, it is advantageous to provide the innerwall of the arc 26 with the illustrated particular wall contour 42. Thewall contour 42 initially has a flat partial region before it mergesinto an arc and thereby forms a small projection. This generates aspecific flow fall-off in a region uncritical for the ultrasonicmeasurement. Thereby an undesired flow fall-off within or close to theultrasonic measurement zone 36 is avoided and thus the measurement isfurther stabilized.

FIG. 2 shows a further embodiment of the ultrasonic measurementapparatus 10 in accordance with the invention. In this respect FIG. 2 ais a three-dimensional outer view, FIG. 2 b is a longitudinal sectionand FIG. 2 c is a sectional illustration transverse to the main flowdirection. Here and in the following the same reference numerals referto the same features or features corresponding to one another.

In the embodiment in accordance with FIG. 1, the measurement module 14is the only add-on module. In contrast hereto, the embodiment inaccordance with FIG. 2 has a bypass module 44 as a further add-onmodule, which is mountable between the base piece 12 and the measurementmodule 14. Initially nothing is changed by the bypass module 44 withregard to the flow supply and to the loop, as the bypass module 44includes two extension pieces 46, 48 for the inflow and the outflow. Ina basic position the bypass module 44 connects the openings 22, 30 ofthe base piece 12 in a pressure-sealed manner to the two straightpartial regions 24, 28 of the measurement module 14 via the connectionpieces 46, 48.

The bypass module 44 is illustrated in FIG. 4 a in a three-dimensionalview and in FIG. 4 b is further illustrated in a separate manner in alongitudinal section. A bypass deflector 50, 52 respectively configuredas a sphere perforated in T-shape forms in a first position, in astraight flow path the connection pieces 46, 48. Through rotation of thesphere the bypass deflectors 50, 52 are transferred into a secondposition in a manner similar to the functionality of a three-wayspherical tap and in its place form a transverse line. This is, forexample, recognizable in FIG. 4 b, wherein the bypass deflector 50,illustrated on the left, is rotated about 90° against the clock-wisedirection and the bypass deflector 52, illustrated on the right, isrotated in the clock-wise direction by 90°. If the transverse line isopened in the second position, then the flow path in the loop and thusto the measurement module 14 is blocked and the fluid instead flowsthrough the transverse line serving as a bypass. The situationcorresponding to the second position is illustrated by a dotted arrow inFIG. 2 c while the illustration otherwise corresponds to the firstposition indicated by the solid arrow. Seals arranged at the spheres ofthe bypass deflectors 50, 52 prevent the flow exit into the respectivelyblocked passage.

For a simplified synchronous actuation of the bypass deflectors 50, 52 alever 54 and a mechanical coupling 56 of the two bypass deflectors 50,52 is provided. This coupling is shown purely by way of example as fourcogwheels in the Figures, to illustrate that the coupling 56 reversesthe rotary direction.

To now exchange the measurement module 14, it is sufficient to actuatethe lever 54 and thus to supply the flow of the fluid through thetransverse line in the second position of the bypass deflectors 50, 52.The measurement module 14 becomes pressure-less thereby and can beexchanged without a problem, for example, with a pre-calibrated exchangemeasurement module. Following the exchange the lever 54 is againactuated so that the first position of the bypass deflectors 50, 52 isrestored and the fluid can be supplied again via the loop through theultrasonic measurement zone 36. The fluid flow must not be interruptedat any point during the exchange.

FIG. 3 shows a further embodiment of the ultrasonic measurementapparatus 10 in accordance with the invention. In this respect, FIG. 3 ais a three-dimensional outer view, FIG. 3 b a longitudinal section andFIG. 3 c a sectional illustration transverse to the main flow direction.

In contrast to the embodiment in accordance with FIG. 2 a further add-onmodule configured as a calibration module 58 is mounted between thebypass module 44 and the measurement module 14. FIG. 5 a separatelyshows the calibration module 58 in a three-dimensional view and FIG. 5 bshows a corresponding longitudinal section.

The calibration module 58 has its own ultrasonic measurement zone 60 inwhich a pair of ultrasonic transducers 62 span a measurement path 64.Additional ultrasonic transducers and thus additional measurement pathsare also possible here. The calibration module serves for deliveringfurther measurement values for the flow velocity as a reference to themeasurement module 14. These measurement values can be used for theplausibilisation of the measurement module 14 or for its calibration.

The calibration module 58 is only an example of the advantageous use offurther add-on modules. For example, in a further embodiment it isplausible to mount an additional measurement module between the basepiece 12 and the bypass module 44 which delivers measurement valueswhile the flow is supplied through the transverse line of the bypassmodule 44 in the second position of the bypass deflectors 50, 52. Thus,during the exchange or the maintenance of the measurement module data onthe flow velocity can still be provided. Different measurement modulesfor different pressures, different accuracy requirements, measurementzones or compositions of the fluid to be measured can be provided in adifferent alternative embodiment.

FIG. 6 shows an alternative variant of a bypass line. In this respect,the bypass line is not provided in its own bypass module 44, but isintegrated into the base piece 12. FIG. 6 a shows the situation duringthe measurement operation. The fluid flows through the base piece 12into the measurement module 14 and back through the base piece 12 intothe pipeline. The bypass line 66 in this respect remains unused.

FIG. 6 b illustrates the alternative situation during maintenance works.The measurement module 14 is pressure-less and can be exchanged withoutdanger and switching off of the flow of the fluid. While the fluid flowsthrough the bypass line 66. Similar to the case of the bypass module 44,bypass deflectors 50, 52 are provided which switch between the two modesof operation of the bypass line 66 on the principle of a three-way tap.

The invention claimed is:
 1. An ultrasonic measurement apparatus (10)for measuring the flow velocity of a fluid which flows in a pipeline ina main flow direction, wherein the ultrasonic measurement apparatus (10)has an ultrasonic measurement zone (36) with at least a pair ofultrasonic transducers (38), an evaluation unit for determining the flowvelocity from a propagation time difference of ultrasound transmittedand received with and against the flow, as well as a deflection unit, bymeans of which the fluid from the main flow direction is deflectable andsuppliable to the ultrasonic measurement zone (36), wherein thedeflection unit (20, 26, 32) forms a loop having an inflow region (24)and an outflow region (28), wherein the ultrasonic measurement zone (36)is provided in the outflow region so that the flow is reproduciblystabilized on entry into the ultrasonic measurement zone (36) such thattransmitted and received ultrasound have at least one component in adirection transverse to the flow.
 2. An ultrasonic measurement apparatus(10) in accordance with claim 1, wherein the loop has a first deflector(20), an arc (26), and a second deflector (32) so that fluid from themain flow direction is deflectable into the inflow region (24) by meansof the first deflector (20), is deflectable from there into the outflowregion (28) by means of the arc (26) and subsequently is deflectableback into the main flow direction by means of the second deflector (32)wherein, in particular, the first deflector (20) and the seconddeflector (32) form a right angle and the arc (26) forms an angle of180.degree.
 3. An ultrasonic measurement apparatus (10) in accordancewith claim 2, wherein the inflow region and the outflow region each havea partial region (24, 28) arranged next to one another and are alignedin parallel to one another, wherein, in particular a plane, whichincludes both straight partial regions (24, 28), is perpendicular to themain flow direction.
 4. An ultrasonic measurement apparatus (10) inaccordance with claim 2, wherein the loop is designed smooth and withoutsharp changes in direction or constricutions, wherein, in particular,the arc (26) has a wall contour (42) which causes a specific flow breakaway in a zone uncritical for the ultrasonic measurement.
 5. Anultrasonic measurement apparatus (10) in accordance with claim 2,wherein a flow rectifier (34) is provided in the inflow region and/or inthe outflow region.
 6. An ultrasonic measurement apparatus (10) inaccordance with claim 2, with a pipe shaped base piece (12) havingconnection regions (16), in particular flanges for the pipeline whichincludes the first deflector (20) and the second deflector (32).
 7. Anultrasonic measurement apparatus (10) in accordance with claim 2, havingat least one add-on module (14, 44, 58) which each have an extensionpiece for the inflow region and an extension piece for the outflowregion and which are connectable to the base piece (12) or to any otheradd-on module (14, 44, 58) and are separable from the base piece (12) orfrom the other add-on module (14, 44, 58), wherein a final add-on module(14, 44, 58) includes the arc (26).
 8. An ultrasonic measurementapparatus (10) in accordance with claim 7, which includes at least oneadd-on module designed as a measurement module (14) having theultrasonic measurement zone (36).
 9. An ultrasonic measurement apparatus(10) in accordance with claim 8, which has the add-on module configuredas a calibration module (58) with at least one pair of ultrasonictransducers (62) for a plausibility check or calibration of themeasurement values of the ultrasonic measurement zone (36).
 10. Anultrasonic measurement apparatus (10) in accordance with claim 7, whichhas an add-on module configured as a bypass module (44) having atransverse line between the inflow region and the outflow region or atransverse line integrated into the base piece (12), wherein a bypassdeflector (50, 52) is provided which in a position selectively closesthe flow to the transverse line and from the transverse line andreleases the flow to the inflow area and from the outflow area and inanother position selectively closes the flow to the inflow region andfrom the outflow region and releases the flow to the transverse line andfrom the transverse line.
 11. An ultrasonic measurement apparatus (10)in accordance with claim 10, wherein the bypass deflector (50, 52) isconfigured on the principle of a three way tap, in particular has twospheres perforated in T-shape with seals which are coupled amongst oneanother and are thus commonly transferrable from the one position intothe other position.
 12. A method for measuring the flow velocity of afluid which flows in a pipeline in a main flow direction, comprising;deflecting the fluid from the main flow direction, supplying the fluidto the ultrasonic measurement zone (36) for the measurement, wherein theultrasonic measurement takes place whilst the fluid is deflected suchthat it flows in a loop, and determining the flow velocity from apropagation time difference of ultrasound transmitted and received withand against the flow from a pair of ultrasonic transducers (38) in anultrasonic measurement zone (36), the loop having an inflow region (24)and an outflow region (28), and wherein the ultrasonic measurement zone(36) is provided in the outflow region so that the flow is reproduciblystabilized on entry into the ultrasonic measurement zone (36) such thattransmitted and received ultrasound ha at least one component in adirection transverse to the flow.